Hydraulic control system



3 Sheets-Sheet 1 Filed Dec. 29, 1944 INVENTOR.

May 8, 1951 T. F. STACY 2,552,067

HYDRAULIC CONTROL SYSTEM Filed Dec. 29, 1944 3 Sheets-Sheet 2 INVENTOR.

BY M f I M 1951 T. F. STACY 2,552,057

HYDRAULIC CONTROL SYSTEM Filed Dec. 29, 1944 3 Sheets-Sheet 3 NVENTOR.

BY W V f ML Patented May 8, 1951 HYDRAULIC CONTROL SYSTEM Thomas F. 'st-acygliqua, Ohio, assignor to The French Gil Machinery Company, .Piqua,

Ohio

Application December 29, 1944; Serial-1N0. 570,276

(]. Bil-52) l 17 Elaims.

This invention relates to a hydraulic motor dc.- vice and especially to the controls: of the motor.

An obg'ect of the invention is to providean improved and simple controlv for hydraulic. circuits by which a double acting hydraulic motor isoperated.

Another .object of the invention is to provideian improved control for a double acting hydraulic motor, with which packing friction opposing the advance of the working member may be reduced without interfering with the operations of the working member, with which the advantages of high pressure in the retracting chamber during the final increment of advance or the workin member may be obtained with a minimum of packing friction on the working member, wi which this result may be obtained automaticaliy, and which will be relatively simple, practical and inexpensive.

Another object of the invention is to provide an improved control .for a hydraulic motor by which the main control valve maybe operated in a simple manner by power, and with Which the pressure that may be maintained by the pump may be varied selectively between predetermined high and low pressures.

Various other objects and advantages will be apparent from the following description of .one embodiment of the invention, and the novel ieatu-res will be particularly pointed out hereinafter in connection with the appended claims.

In the accompanying drawings:

Fig. l is a schematic plan and elevation, with some of the parts in section, of a hydraulic motor and control circuits constructed in accordance with this invention, the controls being in the positions occupied when the motor is in normal, idle position, and the Working member is retracted;

Fig. 1a is a schematic diagram of a part of Fig. 1 showing a slight modification of the controls;

Fig. 2 is a schematic diagram similar to Fig. l and illustrating the action of the various valves while the motor is advancing at rapid closing speed;

Fig; 3 is a view similar to ,Fig. 2, but representing a further period in the advance of the working member of the motor after :the speed of the motor has been decreased to :what is com-- monly called the working speed;

Fig. 4 is a view similar to Fig. 3,, but representing th parts in the positions occupied during a gassing movement; and

Fig. 5 is a view similar to Fig. 4, but illustrating the operation of this hydraulic circuit during a return or retraction movement of the working member.

In the illustrated embodiment of the invention, and referring particularly to Fig. .1, the hydrauiic motor includes a cylinder 1 ha ing open end through which a piston or working. member 12. extends, with the, usual packing :3) pro: vided :between. the shank of this working member or piston 2 and the wall of the chamber of the cylinder l, adjacent to the open .endof the cylinder. "This packin 3 is commonly placed under pressure .or firm contact with the pi ton by 11 adjustable glands as usual in hydraulic This motor is shown as havin a ra id 1 mb r a, and anion pressure adv nc n chamber t, andior this purpose the inner end W ll of the cylinder 1! has a tubular Wall El whi h ext n s towards the op n endof he cylinde The piston or. working member .2 has a recess-=8 open n r mits inner end race. which telescopes loose y -.r the tubular wall 5 s that the workin mem er o piston ,2 has a central post ,or ram '9 which exe tends inside th tubular wall I and terminat s at its nd in a head in which arr es n t n rin s or packing fitting the inner surface "of the wall 1'.

The outer periphery of the working member or piston 2, at its inner end, terminates in a head ll which fits and slides along the inner periphery of the cylinder I. This head l,l may, and preferably does have ,one'or more piston rings 42 in its periphery to provide a seal between the high pressure chamber 6 and the retracting chamber L3 surrounding the working member or piston 2 at the opposite sideof the head .ll' from the high ressure chamber 6, While these piston rings I'Z maybe of any suitable packing material, they are preferably split, metal, resilient rings Similar to the split, metal piston rings commonly employed on the pistons of internal combustion engines and steam engines.

"The high pressure chamber 6 is provided with a prefill opening *3 leading to the reservoir, shown only diagrammatically by the reference H, it being understood that the closed end of cylinder 1 is usually disposed in the reservoir to simplify the connections and to allow any leakage to pass directly into the reservoir. Such .an anrangcment is well known in the art, and there.- fore it has not been illustrated. This passage :l3 is normally controlled by a prefill valve element [5 which has an operatingstem jl s-extending outside of the passage 1.3 into 5a ,position'to-be .engaged and operated by a prefill pilot piston stern I whichoperates in a direction endwiseiof stem [6. in a pilot chamber l8. Aispring l9 acting between a-shoulder on the stem l6 and. a portion of the housing of the-cylinder 1 through which the stem LGgpasses, yieldinglyrges the valve element It into its closed position, ,and a spring 2-0.-surrounding the ,pilot stem 11,, and compressed against an annular disc 26a and a piston head 2% on the stem urges that stem in a retracted direction or a direction away from the end of the stem I6.

Fluid under pressure for the operation of the motor is obtained from a suitable pump 2| which is driven continuously by a motor, not shown, or any other suitable source of power, and it is of the type known as a variable delivery pump with a compensator 22 thereon by which th maximum pressure to be developed by the pump may be automatically controlled. The intake side or port of the pump is connected by a pipe 23 to the reservoir M, and the output side or port of the pump is connected to a pipe 24 having in series therein a pressure relief valve 25 which operated, if a safe operating pressure is exceeded, to connect the pipe 24 to an exhaust pipe 26 leading to the reservoir, so that a dangerously high operating pressure for the pump will be avoided. The pipe 24 has a branch 21 leading directly to the retracting chamber l3, and another branch 28 leading to a main control valve 29.

This control valve has a port 3|] opening into a pipe 3| which leads to the cylinder and pipe 3| has one branch 32 leading to the rapid traverse advancing chamber 5, and another branch 33 leading to the high pressure advancing chamber 6. In series in the branch 32 are two check valves connected in parallel to one another. One of these check valves 34 is an ordinary free check valve which passes fluid from the pipe 3| to the chamber 5, and closes automatically to prevent reverse flow, and the other valve 35 is a pressure relief valve which opens to connect the rapid traverse chamber 5 to the pipe 3| and allow escape of fluid from the chamber 5 only in excess of a selected pressure for which the valve 35 is set. In other words, the check valve 34 passes fluid freely from the pipe 3| into the chamber 5 while valve 35 is set to maintain a desired back pressure in the chamber 5 during the period when fluid is being expelled from chamber 5. These pressure relief valves 35 are well known and available in the open market, and one type of such valve is shown, by way of example, in U. S. Patent No. 2,043,453. r

The other branch 33 of pipe 3| also has a valve 36 in series therein. This valve 36, when in one position, passes fluid from the pipe 3| into the chamber 6 and vice versa, and when in its other position it interrupts fluid flow through the branch 33. The valve element 37 of valve 36 is operated by a pilot chamber 38, in one direction or into one position in which it opens the branch 33 for fluid flow therethrough, and a similar, but smaller pilot chamber 39 at the opposite end of valve 36 serves to cause movement of the valve element 31 into a position in which it interrupts fluid flow from the branch 33. A pipe 40 connects the pilot chamber 39 to the portion of the pipe 33 which is connected directly to the pipe 3 The pilot chamber 38 is connected by a pipe 4| to a valve 42 having a connection 43 to th reservoir and a pipe 44 leading to the pipe 21.

When the valve element 45 of the valve 42 is in one position, such as shown in Fig. 1, the pipe 4| is connected to the pipe 43 and disconnected from the pipe 44. If the valve element 45 is moved into its other position, which would be downwardly in Fig. 1, a land on that valve element would move between the connections to the pipes 4| and 43 so as to disconnect the pipe 4| from the pipe 43, and another land on the valve element would move out of blocking relation to the port opening into the pipe 44, which would connect the pipe 4|, through the valve, to the pipe 44. This valve 42 may be herein later referred to as a pilot control valve, as will appear from the function which will be described later. The valve element 45 has an outwardly extending stem 46 which is connected by a loose connection 41 to one end of a lever 48 pivoted at 45. The other end of the lever 43 has a fork 55.

The working member 2 carries a rod 5| extending in the direction of travel of the member 2, and having a collar 52 threaded in a direction lengthwise thereon for adjustment into different positions along its length. As the working member 2 advances, the collar 52 will engage in the fork 5|] and rock the lever 48 from the position shown in Fig. 1 to the position shown in Figs. 3 and 4, which moves the valve element 45 from the position in which it connect the pipes 4| and 43 as shown in Fig. 1 to a position in which it breaks that connection and connects the pipe 4| to the pipe 44, as shown in Figs. 3 and 4. When the member 2 returns, the collar 52 which has been able to pass beyond the fork 5|] during the advance movement, will again engage the fork and rock the lever 48 back into the position shown in Fig. 1, and then pass on downwardly beyond the fork, as shown in Fig. 1. By this arrangement, the valve 42 will be operated automatically by the advance and retraction of the working member, as will be later explained.

The main control valve 29 has a valve element 53 which moves endwise therein and has an operating stem 54 extending exteriorly thereof in a direction cross wise of the cylinder L as shown in Fig. 1. The valve element 53 is of the balanced type, with spaced lands 55 and 56 which fit the chamber in the valve along which they move. One land 55, has a length or width in the direction of movement of the valve element sufficient to cover and close the port 36 of the pipe 3| when the valve element is in the normal idle position shown in Fig. 1. Another land 56 is narrower or shorter in the same direction so that when the valve element 55 is in the position shown in Fig. 1, with the land 55 crossing the port 30, the port 57 opening into a pipe 58 leading to the pilot chamber l8 of the prefilled valve will be uncovered, and fluid may pass from the pipe 28 into the valve chamber, around the edges of the land 56 and to a port 59 opening into a pipe 60 leading to the reservoir. The valve element 55 occupies an intermediate position in its endwise movement when in the position shown in Fig. 1, and when moved in either direction from that intermediate position, the land 55 will prevent movement of fluid around its edges. This type of valve is well known in the art and its details need not be further described.

Connected in series in the pipe 21 is an auxiliary valve 6| having a valve element 62, a pilot operating chamber 63 at one end of the valve element and a pilot operating chamber 64 at the opposite end of the valve element. The valve element is of the balanced type with spaced lands, and when the valve element is moved in one direction, it connects the retracting chamber l3 to a pipe 65 leading to the reservoir, and when in its other position, which is shown in full lines in Fig. 1, it connects the retracting chamber l3 directly to the pump. The pilot op erating chamber 63 is connected by a pipe 65 to the pipe 3! leaving the main control valve 29, and the pilot operating chamber 64 is connected ceeaoev a? by a pipe 6-! to the pipe 44 leaving the valve 42. When advancing pressure is applied to the adva-ncingchamber of the motor, this pressure in the pipe 3| will be transmitted to the pilot operating chamber -63-to operate the valve element 62 upwardly in Fig. 1- into a position in which the land 63 is disposed between the port openings into the sections of the pipe 21, and another land 59 uncovers the port into the pipe -65 that leads to the reservoir. Thus the valve 61 serves to connect the retracting chamber 1 3 alternately to the reservoir and to the pump depending upon the position of the valve element 68.

The pilot operating chamber 661 is larger in cross-sectional area than that of the chamber "63 so that even though both chambers so and "64 are connected at the same time to the pump-pressure, the pressure in the chamber '64 will, because of its greater area, cause movement of the valve element 62 into the full line position in Fig. l which connects the retracting chamber to the pump. Within the pilot operating chamber M is a helical compression spring in which is compressed between the end of the valve element 6-2 and the end of the .pilot chamber into which the pipe ill opens, so that when pressure in the pipe 63 falls or is released, the spring to will shift the valve element -2 intothe full line position showninFig. l and hold it there.

The outer free end of the stem 54 of the main control valve 2-9 carries a head H which slides in a passage 12 ina small housing 1-3. The head ll abuts against a piston 14 also carried in a housing 73 for limited endwise movement in the same direction as the head H and this piston 14, at its other end, abuts against a flexible impervious and imperforate diaphragm 15 which is clamped across a cavity or chamber it provided in the housing and into which the piston 14 extends. The chamber l6, at the side of the diaphragm :opposite from the piston licommunicates with a pipe 7'! leading to a 3-way valve 18 having a rotor which may be rocked by a handle '59 between two positions. .A passage 85 in the rotor connects the pipe H to an exhaust pipe 81 when inon'e position as shown in Fig. 1, and to a pipe a. leading to asource'8'3 of air under pressure when in its other position. The pipe 82 has a control valve -84 therein.

Alever 85 is pivoted at #86011 a suitable part of the cylinderor press frame, and-one'arm is forked to straddle the valvecstem 54 in an annulargroove 8?, so that by rocking the lever 85,'manually, the valve stem may be shiited in "either direction.

A bell crank lever 538 has one end forked to straddle a reduced shank 89 on the rod 5|, so as to engage beneath a-shoulder 30 on the rod 5|. The lever 38 is pivotedat 91 on a bracket carried by the cylinder l and its other arm is also forked to straddle the valve stem 54 in an annulargroove 9.2. When the working member 2 descends, it will, as it approaches its downward or fully retracted position, engage with the bell crank lever 8 8 .and rock it in a direction to move the valve stem at to the right in Fig. land place the valve element :53 in the intermediate, idle position shown in full lines "in Fig. 1. A collar '93 is fixed on'ithe valve stem 954, anda helicalspring 9 3 surrounding the stem 54 abuts at one end against the collared and at its other end againsta sleeve 95 whichlis slidably'imounted on the valve-stem 5 3.

.A link 95 is pivoted at :81 to the sleeve 95, and at its other-endispivotedat 98 to a link-s 9, which is pivoted at ville-to -a bracket ill-l on the press frame or cylinder -l The link :9'6 may have a handle 402 thereon by which the links 96 and 99 may be moved into or slightly beyond a dead center position as shown in Fig. 1 which is a toggle connection. By rocking the handle )2 .to the left in Fig. '1, the links 96 and .89 may be moved out of a dead center positiomduring which the sleeve will slide along the stem '54 to re lease the pressure on the spring 94. One may then, by manipulation of the lever 85 operatethe valve element 53 of the valve .29 into any of the different positions so as to have complete manual control of the motor. When the handle )2 is moved back into the vertical position shown, the sleeve '55 moves to the left in Fig. l, and places the spring 94 under compression so stem 54 is then responsive to the automatic controls.

The pump 2i of the type shown may have a pilot piston H33 in a pilot chamber I94 which may be supplied with operating fluid under pressure by a pipe which is connected through a valve let to a branch pipe till leading through the pipe id to the pipe section 2-! which connects the auxiliary valve e! to the pump. The valve H16 may have its valve element H38 operated in one direction by a solenoid its and in the other direction by a compressed spring l Ill. When the valve elementv m8 is in the position shown in Fig. 1, into which it has been moved by the spring Hit, it connects the pipe N35 to an exhaust pipe ii! leading to the reservoir. When the solenoid tilt is energized from any suitable manual or autoznaticcontrol, the valve element I 98 will be moved downwardly in Fig. l to compress the spring Hi and the valve element will then disconnect the pipe We from the pipe Ill and, instead, connect it to a branch Hill of the pipe i l. When the solenoid its is energized, and the pipe E55 is connected to the pipe ml, the pump pressure will be applied to the pilot chamber ltd to operate the piston H23, which has a limited movement, and limit the stroke of the pump and decrease the rate of delivery by the pump, so that the speed of operation of the press may be decreased while solenoid 109 is energized. This can be made effective for a breathing operation or for an'initial opening movement of the press after the cycle is completed.

In'Fig. .lais illustrated a slight modification of the construction of Fig 1, in which the rod 46 which is connected to the valve element 45 of the pilot control valve 52, instead of being connected to the lever it for operation by the working memher, is provided with a piston head H2 which reciprocates in a cylinder H3. A compression spring I M in the opposite end of the cylinder I it urges the valve element 45 into the position shown in full lines in Fig. la. When pressure is applied to the upper end of the cylinder I I3, it pulls the valve :rod d6 downwardly in the same manner that the lever 58 moves the Valve rod 46 downwardly in Fig. 1. The upper end of the cylinder H3 is vconnected by a pipe Hi5 to the pipe 66 which leads to "the pilot chamber 63, and pipe Hill has, in seriestherein, a pair of valves I Hi and H l which are connected in parallel to each other, but as a group are in series in the pipe I 5. The valve 1 Hi6 isa :tree check valve which passes fluid in the direction of the arrow or away from the cylinder M3 and closes automatically to prevent reverse iloW therethrough. The valve Ill is a suitable pressure relief valve which prevents flow therethrough in a direction away from the cylinder ii -3 but which opens automatically to pass fluid from pipe =66 to the cylinder H3, whenever the pressure in the pipe 66 exceeds a selected pressure for which the Valve H1 is set.

In the operation of a hydraulic motor with the controls in the positions shown in Fig. 1, the motor is idle with the working member in retracted position. The pump is delivering fluid into the pipe 24 which passes through the pipe 28, valve 29, around the land 56 to the exhaust pipe 56 leading to the reservoir. The arrows in Fig. 1 show the direction of travel of this fluid. The land 56 also uncovers the opening to pipe 58, so that the prefill valve element l may be closed. It will be noted that when the working member 2 approached its lowermost or retracted position, the shoulder 90 on the rod 5| engaged and rocked the bell crank 88 to shift the valve stem 54 to the right, into the position shown in full lines in Fig. 1, during which movement the spring 94 was compressed further.

If one wishes to cause a slight advance of the working member 2, the manual lever 85 may be rocked counter-clockwise in Fig. 1 to shift the valve stem 54 further to the right in Fig. 1, which causes the land 55 to uncover the port 30 and the land 56 to move between the opening into pipe 28 and the groove or port 51. This will cause the fluid from the pump to pass into the pipe 3| and then through one section of the branch pipe 32, free check valve 34 and the other section of branch pipe 32 into the rapid closure chamber 5. Pressure will also pass through pipe 40 to pilot chamber $9 and move valve element 31 upwardly in Fig. 1 to disconnect pipe sections 33.

The working member will then advance, but as soon as the lever 85 is released, the spring 94 will return the valve stem 54 and lever 85 to the position shown in Fig. 1, with the bell crank lever 88 engaging against the shoulder 90 if the movement of the working member is very slight. Usually for this purpose, however, the handle I02 is swung to the left in Fig. 1, so as the break the toggle connection formed by the links 96 and 99, which releases the pressure on the spring 94. The valve stem 54 will then remain in the positions into which it is moved and will have complete manual control of the movements of the working member 2. When the automatic controls are to be used, the links 96 and 99 are in the dead center position shown in Fig. 1, and to start an operation, the attendant operates the handle 19 of the 3-way valve 78, which connects the source of air under pressure to the chamber 16 at one side of the diaphragm.

The air pressure forces the diaphragm to the right from the position shown in Fig. 1, which moves the valve stem 54 to the right until the land 55 in valve 29 uncovers the port 30, as just explained. Fig. 2 shows the circuit arrangement at this time, and in Figs. 2 to 5 the parts have the same references, but the parts are shown in the different positions occupied in a cycle of movement. With the valve element 53 in the righthand position from that shown in Fig. 1, and referring to Fig. 2, the pump delivers fluid under pressure through the pipe 24, pipe 28, valve 29, pipe 3|, pipe section 32, the check valve 34, and pipe section 32 to the rapid closing chamber, which causes an advance of the working member 2. The pressure in the pipe 3| also is communicated through the pipe 66 to the pilot chamber 63, which operates the valve 6| to connect the pipe section 2'! leaving the retracting chamber, to the exhaust pipe 65 running to the reservoir.

The working member moves upwardly rapidly, and since advancing chambers 5 and 6 are disconnected at valve 36, the suction in the high pressure chamber 6 causes the prefill valve l5 to open and allow fluid to pass from the reservoir directly into the high pressure chamber 6 to 00- cupy the space created by the advance of the working member. As the working member advances, fluid is displaced from the retracting chamber |3 which passes directly to the reservoir through pipe 65 so that there will be no back pressure in the retraction chamber that would urge the packing 3 surrounding the piston part of the working member against the piston, with the result that the frictional resistance of the packing 3 on the piston is a minimum.

When the working member reaches the position in its advance where one desires to have a slower advance of the working member, but at a higher pressure, the collar 52, which has previously been suitably adjusted on the rod 5| will, at this time, engage in the fork 50 and rock lever 48 clockwise in Fig. 1 into the position shown in Fig. 3, which moves the valve element in the valve 42 into a position to connect the pipes 4| and 44 so that some of the fluid delivered by the pump into the pipe 44 may now pass through the pipe 44 and valve 42 into the pipe 61 leading to the pilot chamber 64. This causes the auxiliary valve 6| to connect the retracting chamber |3 directly to the pump 2|, so that as the working member 2 continues to move upwardly or advance, the liquid displaced from the retracting chamber, instead of passin through the valve 6| to the reservoir as it did during the previous part of the advance of the working member, will now all pass through the valve 29 with the liquid delivered by the pump, and then will pass through the pipe 3| to the rapid closing chamber.

At the same time that pump fluid is delivered into the pipe 6'! by the operation of the valve 42, some of the fluid passed by the valve 42 will also pass through pipe 4| to the pilot chamber 38 of the valve 36 to connect the pipe sections 33 to thus connect pipe 3| also to the high pressure chamber 6. This condition of the valve 36 is shown in Fig. 1, and the direction of flow is shown by the arrow at the valve 36 in Fig. 3. The fluid delivered by the pump will then be distributed between the two chambers 5 and. 6, and this will break the suction in the chamber 6 so that the prefill valve l5 will be closed by its spring l9. The working member will then be advanced at a slower speed, but with a higher possible pressure throughout the remainder of its movement.

When the working member has completed its movement and one desires its retraction, the valve 19 is operated to connect the pipe 11 to exhaust, and disconnect it from the source of air under pressure. The spring 94 then shifts valve stem 54 in a direction toward the left in Fig. 1, so as to place the land 56 between the connection to the pipe 60 and the groove or port 51, and the land 55 between the port 30 and the opening into the pipe 28. The pump pressure will then be applied by pipe 58 to the pilot chamber l8, tending to open the prefill valve l5, but until the pressure in chamber 6 falls sufliciently, this valve |5 will not open. The fluid from the pump is delivered to the retracting chamber l3 instead of into the pipe 3| as shown by the arrow a in Fig. 4, and since the land 55 moved to the left of the port 30 in Fig. 1, the port 30 is in communication with an exhaust pipe 30a thus releasing pressure in the pipe 3|.

Fluid from the chamber 6 can escape through the pipe 33, valve 36, pipe 3| and valve 29 to the reservoir, and the fluid pressure in the retracting chamber causes a retraction of the working member. The pressure relief valve 35 controls the escape of fluid from the advance chamber 5 so that the retraction of the Working member 2 will not be too rapid, especially at the beginning. If full return movement is desired, this action will continue, but if the retraction of the working member 2 is desired only momentarily to release the pressure in the molds, so that gas in the molds can escape, then as soon as the desired small amount of retraction has occurred, the 3-way valve handle 19 is returned to its former position to have the diaphragm force the valve stem .54 to the right, so as to reconnect the pump to the advancing chambers and a readvance of the working member then follows.

This will continue until the operator again moves the valve handle 79 to cause another retraction of the working member 2. The working member will then begin another return movement which, unless stopped by operation of valve 18 to cause a re-advance, will continue as shown in Fig. 5, the fluid flow being in the direction shown by the arrows at and b in Fig. 5. When the working member 2 reaches the same position in the return stroke at which, during its advance movement, it engaged the fork 50, the collar 52 will again engage the fork '50 and rock the lever 48 back into the position shown in Fig. l. The collar 52 then continues its downward movement as shown in Fig. 5, and when substantially full retraction has occurred, the shoulder 953 engages and rocks bell crank lever 88 to move the valve stem 54 to the right and set the main control valve element 53 in the idle position. shown in Fig. 1.

During the retraction of the member 2, as soon as the pressure in the high pressure chamber-6 fell, due to the release of fluid therefrom through the pipe 33, the pressure in the pipe 58 was able to open the valve l5 so that some of the fluid in the chamber 6 could escape directly through the prefill valve back into the reservoir. This greatly speeds up the retraction. When the main control valve 29 is returned to the condition shown in Fig. 1, the pressure in the pipe 58 is. released, and valve 55 closes. When the valve 512 is returned to the Fig. 1 position during the return of the member 2, the pipe 61 is vented through the valve 62, so that pressure in the pilot chamber 54 is released. The spring 1i], however, keeps the auxiliary valve element 62 in the position as in Fig. 1 because, at this time, the pressure in the pipe 65 is released at the main control valve as. I At the same time that the pipe 5? was vented, the pipe 4! was also vented which released the pressure in pilot chamof valve 36.

When the valve stem 5 is moved to the right to start an advance of the working member 2, the application of pressure to the pipe 3! will place fluid under pressure in the branch pipe 40 leading to the pilot chamber 39, which moves the valve element 3! upwardly in Fig. 1 to disconnect the pipe sections 33. The pilot chamber Si! is larger than chamber 39, so that even though pressure continues in the chamber 39, the application of the same pressure per unit area from the pump to the chamber 38 will cause an operation of the valve element 3'! into the position shown in Fig. 1. Similarly, since the pilot chamber 64 is larger than 83, the admission of the same pump pressure per unit area into both chambers 63 and 64, will result in the movement of the valve element 52 into the position shown in Fig. 1. The pressure in the pilot chamber 63 alone, however, when pilot chamber 64 is vented, will be suffrcient to overcome the spring 10. The solenoid M9 is either manually controlled or controlled by any automatic mechanism, so that delivery of the pump can be changed during movement of the working member 2 when desired conditions have arisen. The manner of control of solenoid M39 is not a partof the invention sought to be covered in this application.

In the modification shown in Fig. 1a, the op-. eration will be the same as explained for Fig. 1, except that the working member will not move the valve 42. When the pressure in the pipe 66, which will be substantially the same as that in the rapid closing chamber 55, exceeds a predetermined, selected pressure due to the working member encountering sufficient resistance, such as caused by engagement with the work, the pressure in the pipe is will rise as the pump'continues to deliver fluid into pipe 3!. This will cause the pressure relief valve H1 to open to pass the pump pressure to the chamber I 13, with resulting compression of the spring H4 and operation of the valve 52 to connect the pump pressure through the pipe -61 to the pilot chamber 54 and to the pilot chamber 38.

A movement of the auxiliary valve 6| to connect the retracting chamber directly tothe pump for the same purpose as explained in connection with Fig. 1, then occurs, and at the same time the valve 36 will connect the pump to the high pressure chamber, so that the member 2 may move forwardly at a slower rate, but at the higher possible pressure. In both Figs, 1 and la, the pilot control valve 42 is operated whena predetermined or selected condition arises in the advance of the member 2, which condition can be either the reaching of a predetermined position as in Fig. l, or a desired pressure on the advancing member 2 as in Fig. 1a.

The lower end of the rod $9 isprovided with a head H8, Fig. 1, so that when the working member 2 has advanced to the maximum distance desired or for which the hydraulic motor is designed, the head H8 will engage with the bell crank 58, rock it counter-clockwise in Fig. l, and move the valve 29 into the intermediate position which stops the advance of the working member and holds it in that position. This is a sort of safety provision, but by making the member H8 adjustable, the press could be stopped at selected positions.

In some instances it may be desirable to control the maximum pressure that may be developed, and which pressure one may desire to maintain for a period of time, and for this purpose a pressure relief valve H9 is connected by a pipe I20 to the pipe section 33 connecting valve 38 to the high pressure chamber 6. This pipe 520 also passes beyond the valve H9 to the pump compensator 22. The valve H9 has a discharge port l2! leading to the reservoir, but this port is normally closed by the valve element I22. The valve H9 is known in the open market as a Vickers hydrocone type Valve, similar to the pressure relief valve 25, one example of which is shown in U. S. Patent No. 2,043,453. With this type of relief valve there is a ball check valve [235, spring loaded to control the pressure at which the relief valve operates. Pressure in 11 the valveon one face of piston I24 connects through a small bleeder passage in the valve piston with a chamber at the opposite face of piston I24. The chamber at the top of the valve which carries the ball check has a larger porting than the bleeder port, and consequently when the required pressure is reached, the ball check I23 will open, relieving the pressure above the piston I24 of the valve, and hydraulic pressure on the underface of the piston will then raise it and open the port I2I.

A pipe I25 is connected to the seat side of the ball check valve I23, or to the chamber at the face of the piston I24 opposite from that where the main pressure is applied, and this pipe is connected through a valve I26 to a pipe I2'I which leads to a suitable pressure relief valve I28 having a discharge port I29 leading to the reservoir. The relief valve I28 is set to open at a lower pressure than that for which the ball check I23 is set to open. The valve I26 is operated into its open position by a solenoid I30 controlled manually or by any suitable automatic control, and into its closed position by spring I3I. When the solenoid I30 is deenergized, spring I3I will close valve element I32 of valve I26, which disconnects the pressure relief valve I28 from the valve IIEI. At such time the valve I23 will unseat when the pressure for which it is set is exceeded by the pressure in the pipe I20 which corresponds to that in the high pressure, advancing chamber 6.

When the valve I23 unseats, valve piston I24 will be moved and port I2I opened. This discharges sufilcient liquid moving to the advancing chamber, while the pump continues to operate, to prevent further rise in pressure in chamber 6. When solenoid I30 is energized, valve element I32 is operated out of the closed position shown in Fig. 1 to connect pipes I25 and I2! which connects the pressure relief valve I28 to the porting in valve II9 that leads to ball check valve I 23. Since valve I28 is set to open at a lower pressure than that of the ball check I23, when this lower pressure is now reached, valve I28 will open and vent the port leading to the valve I23, so as to lower the pressure on that adjacent face of the piston I24 of valve II9. Valve II9 will then open port I2I at this lower pressure, and thus maintain this lower pressure while the pump operates.

Since pipe I20 is also connected to the pump compensator 22, the control of the pressure with the compensator is accomplished by an additional ball check valve I33 shown piped to the compensator by pipes I34 and I35.

It will be understood that various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim:

1. In a hydraulic motor device of the type having a double acting motor with a cylinder and a piston operating in said cylinder and advancing and retracting chambers at opposite faces of a head on said piston, the retracting chamber being disposed at the face of said head nearest the open end of the cylinder, packing around said piston adjacent the open end of said cylinder, a pump, a reservoir, a motor reversing valve, and a hydraulic operating circuit including said chamberspump, reservoir, and valve with a connection from the output side of said pump directly to said retracting chamber uncontrolled by said reversing valve, that improvement in the hydraulic circuit and its control which comprises an auxiliary valve in series in said connection from said pump to said retracting chamber and operable to connect said retracting chamber alternately to said reservoir and said pump separately from said reversing valve, and piston controlled means for operating said auxiliary valve to connect said retracting chamber to reservoir during a first fraction of the piston advance movement and to said pump during the remaining fraction of the piston advance movement, whereby pump pressure will be released from said retracting chamber during said first fraction of the piston advance to reduce packing friction at the open end of said cylinder opposing advance of the piston, and applied to the retracting chamber solely during the final fraction of the piston advance, when high pressures are exerted on said head and balancing of the pressures on any packing on said head is desired.

2. In a hydraulic motor device of the type having a double acting motor with packing between the cylinder and the piston adjacent the zone where the piston leaves the cylinder, a pump, a reservoir, a main control valve and a hydraulic circuit connecting said pump to the advancing and retracting chambers of said motor, with said control valve in the connection between the pump and said advancing chamber, that improvement which comprises a portion of said hydraulic circuit having a direct connection from said pump to said retracting chamber separately from said reversing valve, an auxiliary valve in said connection to said retracting chamber operable to connect said retracting chamber alternately to said pump and to said reservoir, pilot means responsive to the pressure of fluid delivered by the pump to the advancing chamber for operating said auxiliary valve into a position to connect said reservoir to said retracting chamber, further pilot means for operating said auxiliary valve into the position in which it connects said retracting chamber to said pump and having greater pressure force on said auxiliary valve than said first pilot means, and means controlled by the ram travel for rendering said further pilot means effective and ineifective.

3. In a hydraulic motor device of the type having a double acting hydraulic motor with a ram extending from the cylinder and a retracting chamber at the end of the cylinder from which the ram extends, and with packing between the ram and cylinder adjacent said end of said cylin der, a'pump, a reservoir, a connection from the pump to the advancing chamber of the motor with a control valve therein, and another connection from the pump directly to said retracting chamber and by-passing said control valve, that improvement which comprises an auxiliary valve in said another connection and operable to connect said retracting chamber alternately to said pump and to said reservoir, irrespective of the position of said control valve, pilot means responsive to the pressure of the fluid delivered by the control valve to the advancing chamber for operating said auxiliary valve into a position to connect the retracting chamber to said reservoir, further pilot means for moving said auxiliary valve into a position to connect said retracting chamber to said pump and having greater moving power on the auxiliary valve than said first pilot means, a connection from said pump to said further pilot means, a valve in said last connec- 13 tion and operated-by said ram when in a selected zone of its travel for connecting the pum to said further pilot means.

4. In a hydraulic motor device of the type having a working member having a piston head, a cylinder into which the head carrying end of said working member extends, packing at the end zone of said cylinder where said member enters, a rapid traverse chamber for acting on said member at one side or said head to advance it by pressure, a high pressure chamber at the same side of said head for also acting on said member to advance it, a retracting chamber at the opposite side of the head, a pump, a reservoir, a connection from said pump to'said rapid traverse chamber, a control valve in said connection, a branch from said control valve to said high pressure chamber, a valve in said branch connection, and a connection from said pump to said retracti ng chamber separately from said control valve,

that improvement which comprises an auxiliary valve in said last connection to said retracting chamber and operable to connect said retracting chamber alternately to said pump and to said reservoir uncontrolled by said control valve, means responsive to the pressure of thefluid deliver-ed by-said control valve to said rapid traverse chamber for operating said auxiliary valve to connect the retracting chamber to said reservoir, further means for shifting said auxiliary valve to connect said retracting chamber to said pump, and more powerful in its shifting action than said pressure responsive means, and means for selectively controlling said further means, whereby said retracting chamber may be connected to the reservoir to lessen packing friction during anydesired portion of the advance movement of said member, and connected to said pump only while very high pressures on said headare being exerted.

5. Ina hydraulic motor device of the type having advancing and retracting chambers, a working member movable in response to relative pressures in said chambers, a pump, a reservoir, connections from the pump to said reservoir and to each chamber, and a control valve in the connection from the pump to the advancing chamber leaving the connection to the retracting chamber uncontrolled thereby, that improvement which comprises an auxiliary valve in'the connection from said to said retracting chamher and operable between two positions to connect said retracting chamber alternately to said pump and to said reservoir but yieldingly urged into a position to connect said retracting chamher to said reservoir, means responsive to the travel of said Working member and rendered effective when said member reaches a selected intermediate position in its advance for operating said auxiliary valve toconnect said pump to said retracting chamber for the remainder of the advance.

6, In a hydraulic motor device of the type having advancing and retracting chambers, a pump, a reservoir, a connection from the pump to said reservoir and to each chamber, and a control valve in the connection from the pump to the advancing chamber leaving the connection to the retracting chamber uncontrolled thereby, that improvement which comprises an auxiliary valve in the connection from said pump to said retracting chamber and operable to connect said retracting chamber alternately to said pump and to said reservoir, means responsive to the pressure of fluid delivered by said control valve to the advancing chamber for moving said auxiliaryvalve into a position to connect said retracti ng chamber to the reservoir while pressure is applied to the advancing chamber, and additional means for operating said auxiliary valve against the action of said pressure responsive means into a position in which it connects the retracting chamber to said pump, whereby the full pressure of the-pump may be applied to said retracting chamber during a desired portion of the advance movement of said motor.

l. Ina hydraulic motor device of the type having advancing and retracting chambers, a pump, a reservoir, a connection from the pump to said reservoir and to each chamber, and a control valve in the connection from the pump to the advancing chamber leaving the connection to the retracting chamber uncontrolled thereby, that improvement which comprises an auxiliary valve in the connection from said pump to said retracting chamber and operable to connect said retracting chamber alternately to said pump and'to said reservoir, means responsive to the pressure of fluid delivered by said control valve to the advancing chamber for moving said auxiliary valve into a position to connect said retracting chamber to the reservoir while pressure is ap-- plied to the advancing chamber, and platen controlled means for operating said auxiliary valve, against the action of said fluid pressure responsive means, into a position to connect said retracting chamber directly to said pump during a final portion of the advance of said motor.

8. In a hydraulic motor device of the type having a working member having a piston head, a cylinder into which the head carrying end of said working member extends, packing at the end zone of said cylinder where said member enters, a rapid traverse chamber for acting on said member at one side of said head to advance it by pressure, a high pressure chamber at the same side of said head for also acting on said member to advance it, a retracting chamber at the opposite side of said head, a pump, a reservoir, a connection from said pump to said rapid traverse chamber, a control valve in said connection, abranch from said control valve to said high pressure chamber, a valve in said branch connection, and a connection from said pump to said retracting chamber separately from said control valve, that improvement which comprises an auxiliary valve in said last connection to said retracting chamber and operable to connect said retracting chamber alternately to said pump and to said reservoir uncontrolled by said control valve, means responsive to the pressure of the fluid delivered by said control valve to said rapid traverse chamber for operating said auxiliary valve to connect the retracting chamber to said reservoir, and further means responsive to the operation of said Working member for shifting said auxiliary valve against the action of said pressure responsive means to connect said retracting chamber to said pump and for concurrently operating said branch valve to connect said control valve directly to said high pressure chamber, whereby at a selected position in the advance of said working member the pump pressure may be applied to the retracting chamber during the advance of the working member, and thepump pressure also applied to the high pressure chamber concurrently with the application of pump Pressure to the retracting chamber in the advance of the working member.

9. In a'hydraulic motor device of the type having a working member having a'piston head, a cylinder into which the head carrying end of said working member extends, packing at the end zone of said cylinder where said member enters, a rapid traverse chamber for acting on said member at one side of said head to advance it by pressure, a high pressure chamber at the same side of said head for also acting on said member to advance it, a retracting chamber at the outer side of said head, a pump, a reservoir, a connection from said pump to said rapid traverse chamber, a control valve in said connection, a branch from said control valve to said high pressure chamber, a valve in said branch connection, and a connection from said pump to said retracting chamber separately from said control valve, that improvement which comprises an auxiliary valve in said last connection to said retracting chamber and operable to connect said retracting chamber alternately to said pump and to said reservoir uncontrolled by said control valve, means responsive to the pressure of the fluid delivered by said control valve to said rapid traverse chamber for operating said auxiliary valve to connect the retracting chamber to said reservoir, pilot means for operating said auxiliary valve against the action of said pressure responsive means to connect said retracting chamber to said pump, a connection from the pump to said pilot means and having a pilot control valve therein, means controlled by the travel of said working member for operating said pilot control valve into a position to cause said pilot means to connect the retracting chamber to the pump after the working member passes a selected position in its advance, and means also rendered effective by the same movement of said pilot control valve for operating said branch valve to connect said main control valve to said high pressure chamber concurrently with the operation of said auxiliary valve into a position to connect the retracting chamber to the pump.

10. In a hydraulic motor device of the type having a double acting motor with a working member, advancing and retracting chambers for moving said member, a pump, a connection from the pump to the advancing chamber and having a main control valve solely in that connection, and a reservoir with connections from said main control valve and said pump to the reservoir, that improvement which comprises an auxiliary valve solely in the connection from the pump to the retracting chamber, separately from the main control valve, and operable to connect said retracting chamber alternately to said pump and to said reservoir, a pilot device operated by the fluid under pressure passed by said main valve to the advancing chamber, for operating the auxiliary valve to disconnect the pump from the retracting chamber, and a more powerful pilot device controlled by an advancing condition of the motor for overcoming the first pilot device and moving the auxiliary valve to reconnect the pump to the retracting chamber for the balance of the advance of the motor whereby during an advance of said motor the retracting chamber can be connected to the reservoir to reduce the packing friction on the working member of the motor during the advance movement until any desired intermediate condition in the advance of the working member of the motor, and then connected to said pump during further advance of the working member.

1'1. In a hydraulic motor device of the type having a double acting motor with a working member, advancing and retracting chambers for moving said member, a pump, a connection from the pump to the retracting chamber, a connection from the pump to the advancing chamber and having a main control valve solely in that connection, and a reservoir with connections from said main control valve and said pump to the reservoir, that improvement which comprises an auxiliary valve solely in the connection from the pump to the retracting chamber, uncontrolled by the main control valve, pilot means responsive to the pressure of the fluid delivered by the main control valve to the advancing chamber for op erating said auxiliary valve into a position to connect the retracting chamber to the reservoir, and control means rendered effective by said working member at a selected position in its advance for operating said auxiliary valve against the action of said pilot means into the position in which it connects the retracting chamber directly to the pump during further advance movement.

12. In a hydraulic motor device of the type having a double acting motor with a working member, advancing and retracting chambers for moving said member, a pump, a connection from the pump to the retracting chamber, a connection from the pump to the advancing chamber and having a main control valve solely in that connection, and a reservoir with connections from said main control valve and said pump to the reservoir, that improvement which comprises an auxiliary valve solely in the connection from the pump to the retracting chamber, uncontrolled by the main control valve, pilot means responsive to the pressure of the fluid delivered by the main control valve to the advancing chamber foroperating said auxiliary valve into a position to connect the retracting chamber to the reservoir, further pilot means operable on said auxiliary valve to shift it into a position to connect said retracting chamber directly to said pump, a connection from said pump to said further pilot means uncontrolled by said main control valve, a pilot control valve in said last connection, means operated by the motor when a predetermined operating condition has been reached in its advance for moving said pilot control valve into a position to connect said pump to said further pilot means, whereby the motor automatically causes the connection of said pump directly to said retracting chamber at any selected condition in the advance movement of said motor, whereby the packing friction on the motor may be reduced by a release of the pressure in the retracting chamber until the pressure in the retracting chamber serves a useful purpose.

13. A hydraulic motor and controls comprising a cylinder, a piston having a head in and fitting said cylinder and a shank extending from the open end of said cylinder, packing between the piston shank and the cylinder adjacent to the open end of the cylinder, whereby the chamber at the inner end of the cylinder closed by said head will constitute an advancing chamber and the space in the cylinder at the opposite side of said head and around said shank to said packing, will constitute a retracting chamber, a pump, a reservoir, a pilot operated prefill check valve connecting said advancing chamber to the reservoir, a connection from the intake side of said pump to said reservoir, another connection from the output side of said pump to said advancing chamber, a main control valve in said last connection, a connection from the output side of said pump to said retracting chamber uncontrolled by said main control valve, the valve element of said main control valve having an operating stem extending therefrom, mean-s yielding-ly urging said valve stem into a position to cause the valve element to connect the advancing chamber to the reservoir and disconnect it from the pump, and connect the pump to the pilot chamber of said prefill valve to urge the prefill valve to open position, means for moving said valve stem against the action of said yielding means into a position in which the valve element is placed in a position in which the pump is connected to the advancing chamber and disconnected from the pilot chamber, means rendered effective by the piston at a selected position in its retraction for moving the valve stem against the action of said resilient means into an intermediate position in which the valve element disconnects the pump 'from the advancing chamber, and closes the connection from the control valve to the advancing chamber, connects said pump to said reservoir, and uncovers the connection to said pilot chamber, an auxiliary valve in said connection from the output side of the pump to said retracting chamber, means continuously responsive to the fluid pressure delivered by said main valve to said advancing chamber .for operating said auxiliary valve to connect said retracting chamber to the reservoir and disconnect it from said pump while fluid under pressure is delivered to said a'd vancing chamber, and means automatically operative at an intermediate point in the advance travel of said piston for operating said auxiliary valve against the action of said continuously responsive means to connect the pump to said retracting chamber and disconnect the latter from said reservoir during the remaining advance of said piston.

14. A hydraulic motor and controls comprising a cylinder, a piston having a head in and fitting said cylinder, and a shank extending from the open end of said cylinder, packing between the piston shank and the cylinder adjacent 'to the open end of the cylinder, whereby the chamber at the inner end of the cylinder closed by said head will constitute an advancing chamber and the space in the cylinder at the opposite side of said head and around said shank to said packing, will constitute a retracting chamber, a pump, a reservoir, a pilot operated prefill check valve connecting said advancing chamber to the reservoir, a connection from the intake side of said pump to said reservoir, another connection from the output side of said pump to said advancing chamber, a main control valve in said last connection, a connection from the output side of said pump to said retracting chamber uncontrolled by said main control valve, the valve element of said main control valve having an operating stem extending therefrom, means yieldingly urging said valve stem into a position to causethe valve element to connect the advancing chamber to the reservoir and disconnect it from the pump, and connect the pump to the pilot chamber of said prefill valve to urge the prefill valve to openposition, means for moving said valve stem against the action of said yielding means into a position in which the valve element is placed in a position in which the pump is connected to the advancing chamber and disconnected from the pilot chamber, means rendered effective by the piston at a selected position in its retraction for moving the valve stem against the action of saidresilient means into an intermediate posi-- tion in which the valve element disconnects the pump from the advancing chamber, and closes the connection from the control valve to the advancing chamber, connects said pump to said reservoir, and uncovers the connection to said pilot chamber, and an auxiliary valve in the connection from said pump to said retracting chamber and having a valve member operable to connect said retracting chamber alternately to the reservoir and the pump and uncontrolled by said main control valve, means continuously responsive to the pressure of fluid moving into said advancing chamber for operating said auxiliary valve to connect said retracting chamber to the reservoir and disconnect it from said pump, and means controlled by said piston and rendered eiie'ctive automatically at an intermediate point in its advance to operate said auxiliary valve by the pump pressure to overcome said continuously responsive means and reconnect the pump to said retracting chamber and disconnect the latter from said reservoir throughout the remainder of the advance of said piston and until the piston reaches the same intermediate position in its retracting movement, whereby said retracting chamber may be connected to said reservoir during a desired portion of an advance of said piston to relieve the packing friction on the piston adjacent the open end of said cylinder, and connected to the pump only during the part of the advance movement where one desires to prevent danger of jumping of the piston under high pressure or when balancing is desired on the packing between the head of :the piston and the cylinder.

15. A hydraulic motor and controls comprising a cylinder, a piston having a head .in and fitting said cylinder and a shank extending from the open end of said cylinder, packing between the piston shank and the cylinder adjacent to the open end of the cylinder, whereby the chamber at the inner end of the cylinder closed by said head will constitute an advancing chamber and the space in the cylinder at the opposite side of said head and around said shank tosaid packing, will constitute a retracting chamber,,a ,pump, a reservoir, a pilot operated pre'fill check valve connecting said advancing chamber to the reservoir, a connection from the intake side of said pump to said reservoir, another connection from the output side of said pump to said advancing chamber, a main control valve in said last connection, a connection from the output side of said pump to said retracting chamber uncontrolled by said main control valve, the valve element of said main control valve having an operating stem extending therefrom, means meningly urging said valve stem into a position to cause the valve element to connect the advancing chamber to the reservoir and disconnect it from the pump, and connect the pump to the pilot chamber of said prefill valve to urge the 'pi'efill valve to open position, means for moving said valve stem against the action of said-yielding means into ta position in which :the valve element is placedina position in .Whichthfi pumpiis connected to the advancing chamber and discomnected from the pilot chamber, means rendered eflective by the piston at a selected position in its retraction for moving the valve stem against the action'of said resilient "means into an intermediate position in which the valve element dis connects the pump from the advancing chamber, and closes the connection from the control valve to the advancing chamber, connects said pump to said reservoir, and uncovers the connection to said pilot chamber, an auxiliary valve in the connection from said pump to said retracting chamber and operable to connect said retracting chamber alternately to the reservoir and the pump and uncontrolled by said main control valve, whereby said retracting chamber may be connected to said reservoir during a desired portion of an advance of said piston to relieve the packing friction on the piston adjacent the open end of said cylinder, and connected to the pump only during the part of the advance movement where one desires to prevent danger of jumping of the piston under high pressure or when balancing is desired on the packing between the head of the piston and the cylinder, pilot means responsive to the pressure of fluid delivered by said control valve to the advancing chamber for automatically moving said auxiliary valve into a position to connect the retracting chamber to the reservoir during an initial advance of said piston, further pilot means operated by pressure from said pump for moving said auxiliary valve against the action of said first pilot means into a position to connect said retracting chamber directly to the pump, a pilot control valve for connecting said further pilot means alternately to the reservoir and to said pump, and means for operating said pilot control valve in response to a predetermined operating condition of said piston.

16. A hydraulic motor and controls comprising a cylinder, a piston having a head in and fitting said cylinder and a shank extending from the open end of said cylinder, packing between the piston shank and the cylinder adjacent to the open end of the cylinder, whereby the chamber at the inner end of the cylinder closed by said head will constitute an advancing chamber and the space in the cylinder at the opposite side of said head and around said shank to said packing, will constitute a retracting chamber, a pump, a reservoir, a pilot operated prefill check valve connect-'- ing said advancing chamber to the reservoir, a connection from the intake side of said pump to said reservoir, another connection from the output side of said pump to said advancing chamber, a main control valve in said last connection, a connection from the output side of said pump to said retracting chamber uncontrolled by said main control valve, the valve element of said main control valve having an operating stem extending therefrom, means yieldingly urging said valve stem into a position to cause the valve element to connect the advancing chamber to the reservoir and disconnect it from the pump, and connect the pump to the pilot chamber of said prefill valve to urge the prefill valve to open position, means for moving said valve stem against the action of said yielding means into a position in which the valve element is placed in a position in which the pump is connected to the advancing chamber and disconnected from the pilot chamber, means rendered effective by the piston at a selected position in its retraction for moving the valve stem against the action of said resilient means into an intermediate position in which the valve element disconnects the pump from the advancing chamber, and closes the connection from the control valve to the advancing chamber, connects said pump to said reservoir, and uncovers the connection to said pilot chamber, an auxiliary valve in the connection from said pump to said retracting chamber and operable to connect said retracting chamber alternately to the reservoir and the pump and uncontrolled by said main control valve, whereby said retracting chamber may be connected to said reservoir during a desired portion of an advance of said piston to relieve the packing friction on the piston adjacent the open end of said cylinder, and connected to the pump only during the part of the advance movement where one desires to prevent danger of jumping of the piston under high pressure or when balancing is desired on the packing between the head of the piston and the cylinder, pilot means responsive to the pressure of fluid delivered by said control valve to the advancing chamber for automatically moving said auxiliary valve into a position to connect the retracting chamber to the reservoir during an initial advance of said piston, further pilot means operated by pressure from said pump for moving said auxiliary valve against the action of said first pilot means into a position to connect said retracting chamber directly to the pump, a pilot control valve for connecting said further pilot means alternately to the reservoir and to said pump, and means operated by the piston during its advance for operating said pilot control valve to cause movement of said auxiliary valve into a position to connect the retracting chamber to the pump during any portion of the final advance movement of said piston.

17. In a hydraulic motor device of the type having a double acting motor with a working member, advancing and retracting chambers for moving said member, a pump, a reservoir connected to the intake side of the pump, a connection from the pump to the retracting chamber, a connection from the pump to the advancing chamber and having a main control valve solely in that connection, that improvement which comprises an auxiliary valve in the connection from the pump to the retracting chamber uncontrolled by the main valve, and operable to connect said retracting chamber alternately to said pump and to said reesrvoir, means responsive to the fluid pressure in the connection from said main control valve to the advancing chamber for moving said auxiliary valve into a position to connect said retracting chamber to said reservoir, and means for automatically operating said auxiliary valve against the action of said pressure responsive means into a position to connect said retracting chamber to said pump in response to a predetermined operating condition of said motor during its advance.

THOMAS F. STACY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,583,296 Laussucq May 4, 1926 2,103,984 Indge Dec. 28, 1937 2,205,647 Ferris June 25, 1940 2,218,818 Harrington Oct. 22, 1940 2,333,601 Tucker Nov. 2, 1943 2,358,353 Stacy Sept. 19, 1944 2,376,519 Stacy May 22, 1945 2,389,169 Stacy Nov. 20, 1945 2,392,203 Tucker Jan, 1, 1946 

